Li-ion batteries in portable electronic devices typically undergo different charging, discharging and storage routines based on their users. Although it would be advantageous to have relatively long calendar (or storage) life and/or cycle life of the batteries, typically the batteries have limited calendar and cycle lives partly due to chemical degradation of the battery and mechanical degradation caused by the breathing nature of electrodes, changing their thickness upon lithium intercalation and removal. For example, although Li-ion batteries employing a manganate-spinel-based cathode material generally have higher safety, higher power capability and lower manufacturing cost, compared to those employing a LiCoO2-based cathode material, they have relatively lower cycle and calendar lives. Also, among the same type of batteries, their calendar and cycle lives can be different from each other depending upon charging, discharging and storage routines that they undergo based on their users.
Two properties generally are to be considered for the calendar life of a battery. The first property relates to lost capacity of a battery during storage via self discharging. It is well known in the battery industry that a battery that is stored without ability to charge may partially lose its charge. The level of charge loss generally depends on factors such as chemical stability, temperature and storage time. Li-ion batteries are examples of such batteries that generally lose their capacity during storage via self discharging. The lost capacity of a Li-ion battery may be measured as the relative state-of-charge change (or voltage change) that a battery undergoes during storage. The second property relates to recoverable capacity and permanent degradation of a battery that is non-recoverable. The recoverable capacity can be measured by relating initial capacity during a full charge/discharge cycle to that of a full charge/discharge cycle of a battery that has been stored. The lost capacity of a battery is believed to be related to chemical degradation of the battery during storage, which is different from the degradation caused by cycling a battery. The degradation caused by cycling a battery is believed to include degradation caused by the breathing nature of electrodes. Regardless, degradation of batteries consequent to prolonged periods of use is a pervasive problem for many electronic devices, particularly those that employ lithium-ion batteries.
Therefore, there is a need for developing methods for increasing the calendar life and/or cycle life of batteries, such as Li-ion batteries.